The only circumstance in which the dependent claim would be significant would be if the broader claim was invalidated. E.g., the broadly defined speed control system of claim 5 is found to be obvious over the prior art, but a speed control system additionally including the SMPH feature was non-obvious. In this case the patent would only cover a speed control system with the SMPH feature.
Controlling speed based upon feedback from an optical incremental encoder is absolutely prior art. It is done all the time in industry from everything from conveyors to 6 axis robots. Converting to a speed unit of measure is also common under the same senario. The math is the same regardless if you're displaying "Scale Miles per Hour", Feet/minute or Farthings per Fortnight. The variables become the pulses/revolution and the relational speed constant. Cruise control on your car works exactly the same way.
The description of taking an input and calculating an output value that is a correction to an error to setpoint is classic PID (Proportional Integral Derivative) control. It's been around for more than 100 years.
http://en.wikipedia.org/wiki/PID_controller
That said, it would take someone with the money and determination to challange it in court to get it invalidated. Given the tight margins I'm seeing in this industry, I would not expect to see this challanged. The only senario I could imagine is if company "X" ignores the MTH patent and does it, then MTH would sue (big surprise) and in my opinion MTH should lose the suit.
BTW, no I'm not a lawyer but I am a control engineer. I have done what is described in this patent hundreds of times on a wide variety of equipment.
Gilly
Please don't take this as MTH bashing. I like MTH. I do however, think that this is an invalid patent.
